Articles you may be interested inTheoretical analysis of enhanced second-harmonic generation based on a self-formed antiguide structure

We present a mode field analysis of the second-harmonic electromagnetic wave that radiates from a nonlinear core bounded by a dielectric cladding. With this analysis the ultimate performance of the organic crystal-cored single-mode optical fiber waveguide as a guided-wave frequency doubler is evaluated through the solution of nonlinear parametric equations derived from Maxwell’s equations under some assumptions. As a phase-matching scheme we consider a Cerenkov approach because of advantages in actual device applications, in which the phase matching is achievable between the fundamental guided LP01 mode and the second-harmonic radiation (leaky) mode. Calculated results for organic cores made of benzil, 4-(N, N-dimethyl-amino)-3-acetamidonitrobenzen, 2-methyl-4-nitroaniline, and 4′-nitrobenzilidene-3-acetoamino-4-metxianiline provide useful data for designing an efficient fiber-optic wavelength converter utilizing nonlinear parametric processes. A detailed comparison is made between results for infinite and finite cladding thicknesses.

Frequency doubling of infrared coherent radiation in a planar waveguide loaded by an organic thin film is described. By using a strongly nonlinear crystal, such as 2-methyl-4-nitroaniline, as the loading organic material, more secondharmonic radiation can be expected than that reported in a proton-exchanged or Ti-diffused LiNbO(3) waveguide. The electromagnetic field analysis shows that the selection of a cover material that bounds the surface of the organic film is important in fulfilling the Cerenkov condition.

For the wavelength conversion by the Čerenkov‐radiation scheme in a nonlinear optical waveguide, a novel device structure is proposed which improves the efficiency and the characteristics over the conventional ones. An optimization of such a device structure is attempted. In this waveguide structure, a transverse distribution is provided not only for the linear refractive index but also for the nonlinear susceptibility. This paper shows that the second harmonic generation in a proton‐exchanged LiNbO3 waveguide is expected to be enhanced by more than an order of magnitude by changing the region near the surface of the conventional structure into a domain‐inverted layer. Further, if the thickness of the domain‐inverted layer is controlled precisely, the selection of the guiding‐layer thickness (or the refractive index profile) can be relaxed substantially. This feature would be extremely attractive in designing actual device structures.

A three‐dimensional (3‐D) nonstationary analysis method is proposed for the quasi‐phase‐matched (QPM) second‐harmonic generation in an optical waveguide with a periodic domain‐inversion structure. In this method, a 3‐D modeling of a waveguide‐type QPM is made possible by combining the mode coupling theory with the weighted‐index method (WIM) which is a highly accurate approximate analysis method for an optical channel waveguide. As an example of application, the effect of the channel dimensions on the conversion efficiency is studied for a proton‐exchanged LiNbO3 waveguide with a rectangular‐shaped inverted domain. The actual domain‐inversion shape is expected to be different, depending on the type of substrate material and inversion process. The present method is also applicable to an arbitrary inverted‐domain shape. Hence, the method is considered to be extremely useful for an actual device design.